The present invention relates to a grinding jig for attachment on an edge tool to be ground on a rotating grindstone in a grinding machine, having a support means in the vicinity of the grindstone.
Such a grinding jig is used for holding the tool at a constant angle towards the grindstone, so that the tool edge gets a single bevel without any extra and non-desired bevels, but also for holding it steadily sideways for obtaining a clean and sharp edge.
A conventional grinding jig may be an open yoke with a certain width. The tool is to be inserted in the yoke and is clamped therein by a screw. At grinding, the rear side of the yoke or the side of the yoke facing from the grindstone and the tool shank is applied against the support means, usually in the form of a cylindrical support bar.
The opening in a jig suitable for grinding curved gouges may preferably have a triangular shape, so that the tool shank is clamped by the screw against the V-shaped bottom of the jig.
By the geometry at grinding, the tool shank needs to have a certain minimum length, in practice say 75 mm at an edge angle of 20xc2x0. Many woodcarving tools, especially palm-held tools, have a shorter length and accordingly cannot be ground with this jig.
This jig gives the tool a fixed angle. However, the direction of the tool has to be controlled by keeping the jig at all times in contact with the support bar during the grinding operation. Experience and a certain skill are required from the operator, whose attention has to be directed to this.
Further, the pressure from the screw is distributed over the entire bottom surface of the jig via the tool shank. If the shank surface is not straight, but convex, the shank rides in the middle of the jig under the screw, which means that the clamping is not stable.
The above drawbacks are according to the invention eliminated in that the jig is split by having a base portion and two parallel open yokes extending therefrom, the screw for clamping the tool against the bottoms of the yokes being provided in the base portion between the two yokes.
Hereby the grinding jig will provide guidance on both sides of the support bar, as the jig at grinding is placed astraddle of the support bar with the two yokes at either side of the bar.
The following advantages are obtained:
Tools with a shank length down to only 45 mm at a 20xc2x0 edge angle can be ground, i e practically all woodcarving tools.
The jig automatically controls that the tool is perpendicular to the grindstone. The attention of the operator can be concentrated on the tool edge engagement with the grindstone and not to keeping the tool perpendicular to the grindstone.
The jig locks the tool in both axial directions in relation to the support bar.
The tool is firmly clamped in the jig by the fact that it is supported by the preferably V-shaped bottoms of the two yokes.